D. Gray-man

D.Gray-man is the story of Allen Walker, who roams a fictional 19th century Earth in search of Innocence, a mysterious substance used to fight demons called akuma. Allen Walker travels to the headquarters of the Black Order, a group of exorcists out to destroy the Millennium Earl, the creator of the akuma. Allen is already a strong exorcist and wants to join the Black Order, but he might not even survive getting past the guard!